This invention relates to a laser cutting machine which can control the configuration of a section formed in a workpiece by a laser beam, and more particularly to a laser cutting machine in which a section formed in a workpiece by a laser beam is not tapered.
CO.sub.2 lasers, YAG lasers, etc. have been put in practical use industrial for cutting operations. In general, in such a laser, a laser beam condensed by a machining lens is applied to a workpiece positioned near the focal point. Under this condition, the workpiece or the laser beam is moved to cut the workpiece.
FIGS. 5 and 6 are sectional diagrams showing examples of the configuration of sections formed in workpieces by a CO.sub.2 laser beam according to a conventional method. In the case of FIG. 5, a metal workpiece (e.g. a soft steel plate about 9 mm in thickness) is cut; and in the case of FIG. 6, a non-metallic workpiece (e.g. a wooden workpiece about 20 mm in thickness) is cut.
A laser beam 2 from a laser oscillator is applied to a machining lens 3, so that it is condensed as indicated by the one-dot chain line. The laser beam thus condensed is applied to the metallic workpiece 4a or non-metallic workpiece 4b. In this connection, it is well known in the art that the following phenomena occur: In the case where a metallic workpiece 4a at least 4.5 mm in thickness is cut, its cut is tapered in section in such a manner that the cut width on the laser incidence side is larger with a taper angle of 1.degree. to 2.degree.. In the case of a non-metallic workpiece, its cut is tapered in section in such a manner that, in contrast with the case of the metallic workpiece 4a, the cut width on the laser incidence side is smaller.
The laser cutting method is generally employed in place of a method of machining thin plates using a turret punch press or the like. However, when used for forming mechanical parts of about 4.5 to 12 mm in thickness (particularly for forming gears or precision mechanical parts), the above-described tapered section may be an unacceptable. This difficulty is an obstruction to an increase of the range of application of the laser cutting method.
In order to overcome the above-described difficulty, a laser cutting machine has been proposed in which a laser beam is inclined and rotated by a three-dimensional laser cutting machine (see for instance Unexamined Japanese Patent Publication No. 174291/1985). In addition, a laser cutting machine has been proposed in which a machining lens is moved to incline the laser beam (see for instance Unexamined Japanese Patent Publication No. 5693/1989).
However, the former laser cutting machine suffers from difficulties that it is expensive, and it is difficult to provide a machining locus (or machining path) high in accuracy because the machine is intricate in mechanism and in control. The latter laser cutting machine is also disadvantageous in that, similarly as in the above-described laser cutting machine, it is expensive, and it is difficult to provide a machining locus high in accuracy, because generally in a laser machining operation it is necessary to jet machining gas from a nozzle coaxially with the axis of the concentrated laser beam.